Dental filling

ABSTRACT

A METAL ALLOY DENTAL FILLING CONSISTING OF ABOUT 99.7 TO 99.95 PARTS PURE GOLD ALLOYED WITH ABOUT .05 TO .30 PART CALCIUM IS CONDENSED IN A PREPARED TTOTH CAVITY. THE ADDITION OF CALCIUM TO PURE GOLD RESULTS IN A SIGNIFICANTLY HARDER FILLING.

United States Patent O 3,667,937 DENTAL FILLING Clyde E. Ingersoll,Tonawanda, and Reginald V. Williams,

Sr., deceased, late of Buffalo, N.Y., by John A. Williams and ElizabethP. Williams, executors; said Ingersoll assignor to Williams GoldRefining Incorporated, Buffalo, N.Y. No Drawing. Filed Oct. 7, 1970,Ser. No. 78,990

Int. Cl. C22c 5/00; A61k 5/02 U.S. Cl. 75-165 2 Claims ABSTRACT OF THEDISCLOSURE A metal alloy dental filling consisting of about 99.7 to99.95 parts pure gold alloyed with about .05 to .30 part calcium iscondensed in a prepared tooth cavity. The addition of calcium to puregold results in a sig nificantly harder filling.

BACKGROUND OF THE INVENTION This invention relates to dental fillingalloys and, more particularly, to gold alloys used as dental fillings.

It has been known for many years that pure gold in various forms can becondensed into a prepared tooth cavity to form a filling ofexceptionally long life. Gold has many qualities admirably suited fortooth fillings, but a pure gold filling does not exhibit the desireddegree of hardness and furthermore tends to lose some of its limitedhardness over a periodof time. A pure gold filling also is deficient inabrasion resistance. It has been proposed to alloy small quantities ofother metals to pure gold, in an effort to produce a dental fillingwhich retains the desirable properties of gold while providing betterabrasion resistance and increased hardness. However, such prior artefforts have not been particularly successful. By way of example,platinum and tin have been proposed as additives. However, gold alloyedwith platinum alone is not sufficiently hardened. Tin renders the goldalloy non-cohesive, with the result that cold welding of successivelayers could no longer be effectively accomplished. Also, some additivesrender the gold alloy too hard, so that condensation cannot produce adense, porosity free, finished filling.

In addition, it has been recognized in recent years that pure gold, ifstressed sufficiently during deformation, will anneal or soften at roomtemperatures. Accordingly, it is desirable to find an additive which,when combined with pure gold, will preclude this undesirableself-annealing of gold and will form a gold alloy of the desired levelof hardness and abrasion resistance while not so hard initially as toprevent proper condensing into the tooth cavity.

SUMMARY OF THE INVENTION detailed description 3,667,937 Patented June 6,1972 DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT A dental fillinggold alloy should be sufiiciently malleable and cohesive initially topermit ready condensation by compression into a prepared tooth cavitywith the usual dental office equipment to produce a dense, impermeablefinished filling. The alloy should possess the ability to form a strongbond between successive layers of the alloy and produce a fillingexhibiting the requisite degree of hardness and capable of withstandingabrasion forces normally encountered in the human mouth due to biting,chewing, brushing and other frictional engagement against or between theteeth. It is particularly important that the alloy retain the desireddegree of hardness over a long period of time thereby avoiding frequentreplacement. All of this is accomplished by the dental filling alloy ofthe present invention which consists primarily of pure gold to which isadded a minor amount of calcium. We have found that gold alloy havingthe above properties can be obtained by alloying these components withinthe following ranges, expressed in percentages by weight:

Gold: 99.7% to 99.95% Calcium: .05%.to 30% The proportion of the abovealloying elements may be varied within the limits specified, thepreferred alloy for most dental fillings comprising about 99.85% puregold and 0.15% calcium. However, it should be appreciated that in somedental filling applications, greater strength is required than in otherapplications. Accordingly, where greater strength is required, thecalcium content will be increased within the limits specified above.However, a calcium content above .3% will excessively harden the goldalloy, causing it to become brittle and thereby susceptible to fracture.A calcium content below .05% on the other hand, will not appreciablyaffect the properties of the pure gold in the alloy.

An important feature of the present invention is that the calciumpresent in the gold alloy is effective to preclude self-annealing of thegold component and thereby of the condensed filling. It has recentlybecome known that if pure gold is stressed sufficiently during itsdeformation in the cavity, it has a tendency to anneal or soften at roomtemperature. Calcium has a crystal structuresufficiently different fromthat of gold so as to block selfannealing of the gold constituent. Whilecalcium, like gold, is face centered cubic in structure, it has asubstantially different lattice constant (5.57 as compared to 4.0783 forgold) so as to effectively block self-annealing of the latter.

This large difference in lattice constant also facilitates thecompression or cold working of the alloy in place in the tooth cavity.During condensation, the gold alloy is hardened to a significantlygreater extent than pure gold would be. For example, fillings made ofpure gold foil by six dentists averaged 70.8 Brinell hardness while goldalloy fillings made in accordance with the present invention placed bythe same six dentists averaged 90.9 Brinell hardness. The low solidsolubility of calcium in gold adds considerably to the cold workingeffect of the alloy.

The gold-calcium alloy of the present invention preferably iselectrolytically precipitated into a powder form. The powder iscollected, washed, dried, formed into strips or sheets and sintered toform a cohesive, spongy mass. This spongy mass can be utilized in suchform or, during the sinte'ring operation, a veneering coat of pure goldor gold-calcium foil can be applied. Although the goldcalcium alloy ispreferably formed into a powder by the above mentioned electrolyticprecipitating technique and then converted into a spongy mass, it shouldbe understood that the gold-calcium alloy can be produced in variousforms within the purview of this invention. For

example, it can be beaten into a =foil or leaf, if desired.

In use, pieces of the alloy of this invention are placed in a preparedcavity and condensed with an appropriate condenser. Further pieces ofthe alloy are added which, on condensing, cold weld with previouslyadded pieces to produce a filling. The addition of calcium to pure goldin accordance with this invention results in as much as a 30% higherhardness in the condensed filling.

A preferred embodiment of this invention having been disclosed indetail, it is to be understood that this has been done by Way ofillustration only.

What is claimed is:

1. A dental filling produced by condensing in place within a preparedca-vity successive layers of an alloy consisting of gold in an amountranging from 99.7% to 4 99.95% by weight and calcium in an amountranging from 0.05% to 0.30% by weight.

-2. A dental filling as set forth in claim 1 whereinthe alloy consistsof about 99.85% gold, the remainder being calcium.

References Cited UNITED STATES PATENTS 2,947,623 8/1960 Lincoln 75165U.S. Cl. X.R. 32.-l5

